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As shown in the picture...
I've always heard from manufacturers that all venting must slope towards the unit, and option #2 was the only pictures they had (providing you don't just come straight out, or into some form of termination kit).

Today I was told that option #1 will work, and also told option #1 will freeze up. The lenth of the run outside of the house isn't very far, lets say around 12" or less for the sake of using numbers.

Option #1, everything slopes towards the unit (inside) accept for the last short run thats outside (after the last elbow), that length of pipe slopes away from the house to allow everything to drain out of the pipe.

Option #2, everything slopes towards the unit (inside) all the way.

Lets also throw in the variable of either both ways insulated, or both ways uninsulated.

Answer options, will work, will work but it's right, won't work, or any variety inbetween.

I know there are many answers that aren't right, but aren't really wrong, just bad practice. I'm curious to see what ya pro's have to say.

My personal answer is #2 is best (since I've seen it in so many installation books), but #1 would work in a pinch. I really don't see it icing up too bad if it's a short run.

It must go up 1/4 per linear foot & the shortest route possible.On option #1 I don't know,never tried it but I looked it up couldn't find out what would happen but it said you must install a drain trap tee must be located in horizontal section as close to the furnace flue outlet as possibe 3"permanent trap loop 18" down min.I don't do this I let it go back to the furnace & then pump it out.

#2 is how I always terminate flue pipes but I know of a few houses that carpenters have built decks over my flue pipes and turned them like #1. It will work because I drive buy one of them every day and its been like this for two years. The water will drain out before it gets a chance to freeze and what little stays is melted by the next heat cycle.

Amick.

The only correct answer to this question is in the I&O manual of the furnace.

As far as pitching the outdoor pipe away from the house, well, what good does that do if the rest is pitched to the unit, like it's supposed to be? The only thing leaving that pipe is condensation, and, if piped correctly, it's being thrown 6-8 away from the house as a vapor, with the gases of combustion.

I pitch everything to the unit.

Most I&Os will actually tell you the configuration, min and max distances apart of the fresh air and exhaust. If you do what they tell you, you'll never be wrong.

Vent Termination

As posted aleady - (according to the equipment Mfg. I & O). If the I & O is not with the equipment (here) our inspectors will not pass the job. I have never seen option 1 used on a furnace install. Which Mfg. showed option 1 ?

No manufacture showed option #1, it was an idea I thought up. One of them situation where there's no right answers, h/o doesn't want any new holes punched in the house, and the new addition's roof's eve covers most of where the old pipes come out. H/o wanted the pipes dropped down below the eve and terminated there.

I talked with a knowledgable guy at the supplier I go to often, he said #1 would work just as good as #2. Talked to my boss and he went balistic and said that option #1 would freeze up in a big hurry.

Just another one of them jobs there's no right answers to anything. H/o wants one thing, boss wants another, some ideas are wrong and I'm left in the middle to try to keep everyone happy lol.